Generally, a hydraulic excavator as a representative example of a construction machine largely constituted by an automotive lower traveling structure, an upper revolving structure mounted on the lower traveling structure to be capable of revolving thereon, and a working mechanism mounted to be capable of lifting and tilting in a front side of the upper revolving structure.
The upper revolving structure is provided with a revolving frame forming a support structure, a floor member which is provided on the revolving frame and on which an operator's seat is mounted, and a cab box which is provided to cover the periphery and the upper side of the floor member, forms an occupying space therein, and has a door openable and closable on an outer surface in one of the right-left direction.
Here, an example of the hydraulic excavator includes a small-sized hydraulic excavator so-called a mini-excavator. In the small-sized hydraulic excavator, the lower traveling structure is set to have a small width dimension in such a manner as to be capable of performing a work even in a narrow work site such as a residence area or an alley. On the other hand, the upper revolving structure is formed in a compact size not to protrude largely out of the narrowly-wide lower traveling structure at the revolving movement. Therefore, in the small-sized hydraulic excavator, the floor member and the cab box are downsized, and an installation space for devices mounted on the floor member, for example, an indoor unit in an air-conditioning unit for supplying conditioned air to an occupying space is also made small.
Therefore, in regard to the small-sized hydraulic excavator, there is known a hydraulic excavator in which a concave portion is formed in a position of a foot rest part in the floor member on which an operator seated on an operator's seat places a foot, an indoor unit is accommodated in the concave portion and an upper side of which is covered with a closing plate (for example, refer to Patent Document 1 and Patent Document 2).
On the other hand, since the foot rest part of the floor member has a relatively small floor area, it is difficult to ensure a space for accommodating the indoor unit. Therefore, there is known a small-sized hydraulic excavator of a different type in which an indoor unit accommodating space is formed under an operator's seat mounting portion for mounting the operator's seat and an indoor unit is accommodated in the indoor unit accommodating space (for example, refer to Patent Document 3 and Patent Document 4).
In this case, the operator's seat mounting portion is formed to be high for ensuring the indoor unit accommodating space in a low side thereof, and as a result, a mounting position of the operator's seat also becomes high. Therefore, when the operator is seated on the operator's seat, a head clearance between a head of the operator and a ceiling of the cab box is made small, worsening a working environment of the operator because of a constrained feeling. The cab box is required to be large-sized for ensuring this head clearance.
Further, there is known an excavator with the other conventional art in which an opening is provided in the floor member to be positioned under the operator's seat mounting portion for restricting the mounting position of the indoor unit to a low position, a concave-shaped cover that is recessed to a lower side is mounted to this opening, and the indoor unit is accommodated in the concave-shaped cover. By arranging the indoor unit in the concave-shaped cover, the mounting position of the indoor unit can be restricted to the low position (for example, refer to Patent Document 5).